I want to replace my stock REO50's with Michelin PS2's. The PS2's in the 225\255 give me only half the amount of tire stagger over stock. (Same story for the Falken 615's, AD07's, etc.) This will increase oversteer and I want to keep that the same.

Do I need to install a stiffer AP1 front swaybar or are there reasonable alignment adjustments I can make to keep the balance of the car the same?

 

You could do a narrower front tire if one is available from the manufacturer of your choice, The OEM RE 050's have a 6.7" tread width. That is like a 205 from some manufacturers. You could remove the rear bar completely, or go with a stiffer front bar. I personally wouldn't do anything until after I put the new rubber on and then DROVE the car to see how the balance differed from stock. You can turn your S2000 into an understeering pig for a 1000 miles or so simply by putting on new rear (stock) rubber and leaving on some 12,000 mile heat cycled fronts on the car.

 

The 225/45R17 front and 255/40R17 rear should do the trick. Michelin does not list the contact patch on their tires but it would be the best sizes.
If I can help let me know.